High speed signals in communication systems are often corrupted by signal timing instabilities, typically referred to as signal jitter. Signal jitter can include various components, such as random jitter, data dependent jitter, and periodic jitter. The periodic jitter can be characterized by determining the frequency of the periodic jitter, which is useful for identifying the source of the periodic jitter.
Sampling systems, such as equivalent-time sampling oscilloscopes, are well-suited for characterizing high speed signals that have repetitive bit patterns. Highly stable time bases within the sampling systems also make the sampling systems suitable for characterizing periodic jitter. However, the sampling rates of the sampling systems are typically lower than the bit rates of the high speed signals and the frequencies of the periodic jitter that may be present on the signals. This under-sampling results in aliasing, which impairs the ability of the sampling system to characterize periodic jitter. Particularly, this aliasing makes it difficult for the sampling system to distinguish between actual signal components of the periodic jitter and aliased signal components that result from the under-sampling. Accordingly, there is a need for a scheme for characterizing periodic jitter that distinguishes actual signal components of periodic jitter from the aliased signal components of the periodic jitter.